Direction indicating device



2 Sheets-Sheet 1 o -..0F53 g5 i 3i w46 B.'D. LOUGH| IN DIRECTION INDIQATING :DEVICE Filed Sept;A 15, 1944 INVENTOR Dec. 3l, i942@ DIRECTION` INDI CAT'ING DEVICE `F'iled Sept. l5, 1944 www?" 2 Sheets-Sheet 2 *I *2 FIG. 2

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F|G.3 Tlmen-` /45 LTU I\IORTIISOLITIIo RECEIVING SYSTEM c 46m I5 EAST-WEST o f PULSE RECE'V'NG TRANSM'TTER S GENERATOR SYSTEM o I INDICATOR.

FIG.4

INVENTOR Patented Dec. 31, 1946 f unire -1 29eme@ DIRECTON INDICATING DEVICE Bernard n. Loughlin, Bayside, N. Y., assigner, by mesne assignments, to Hazeltine Research, inc., Chicago, Ill., a corporation of Illinois Application September 15, 1944, Serial No. 554,233

(Cl. Z50- 11) 13 Claims. 1

The present invention relates to direction-indicating systems of the type adapted for use as an aid in the navigation of a mobile craft and, particularly, to such systems of the type Which utilize spaced wave-signal radiators.

The majority of the prior wave-signal systems utilized as an aid in navigation may be roughly divided into several classes. One class, used largely for marine navigation, is the radio direction-finder system which employs a movable directive receiving antenna, usually of the loop or Adcock type, by which to obtain directional information from signals radiated between the mobile craft and stations of known xed position. In the absence of knowledge of the general position of the craft from one such station, as might occur during blind flight of any aircraft, two such stations when suiciently widely spaced furnish suicient information with the aid of a compass to ascertain position, free from ambiguity, by calculation cr by some plotting process. Where compass bearings are not available to a mobile craft or cannot be relied upon, at least three widely -spaced stations are necessary for the ascertainment of position of the craft. This system has the disadvantages that it not only requires at least two and possibly three Widely spaced systems, but also that it is not in general adapted rapidly and easily to provide desired position indications. Moreover, only one craft can be served at a time by the system.

The prior systems most extensively used in air-craft navigation are of the complementarysignal or equi-signal-locus class, employed with predetermined deiined courses. These directional radio beacons, or radio range beacons, may be considered direction-indicating systems in the limited sense that the defined courses have predetermined fixed directional relations with a terrestrially located radiating system. Systems of this character are subject to the serious limitation that they may provide indications of but a relatively small number of divergent courses. Additionally, their operation is premised upon received wave-signal intensities which are affected by many factors, such as terrain and atmospheric fading, with the result that this type of system is subject to errors introduced by these extraneous factors.

Other proposed prior art systems have numerous disadvantages and limitations by virtue primarily of the fact that they depend upon the intensity of the received wave-signal energy to provide the direction indications. Thus, any factor affecting the wave-signal intensity, such as unevenness of the terrain surrounding the transmitting antennas or atmospheric fading, seriously impairs the accuracy of the system. Accuracy of indication is likewise impaired by changes of the relative intensities or phases of the wave signals applied to transmitting antenna systems, or by relative changes of the amplitudes or phases of the modulating signals.

It would be desirable that direction indications through 360 degrees, and without ambiguity, be provided by the use of only one station of fixed location. It would further be desirable that the system be one of the pulse-modulation type which has the important advantages that it permits the transmitting equipment of the system to operate with high peak-power output greatly exceeding its average power-outputl capabilities, thus operating with high-power gain, and additionally permits a transponder type of operation. In the latter mode of operation, the process by which direction is determined is initiated by an interrogating signal which is transmitted from the direction-indicating staton to the station `which radiates the wave signals used in providing the direction indication. The interrogating signals when received by the latter station initiate and control its operation so that direction-indicating signals are radiated only when interrogating signals are received, thus minimizing possible interference with adjacent transmitting channels used for other purposes and increasing the element of secrecy which is of importance in military applications.

It is an object of the present invention to provide a new and improved direction-indicatirer system which is free of one or more of the abovementioned disadvantages and limitations of prior systems of this type.

It is a further object of the invention to provide a new and improved direction-indicating svstem which possesses one or more of the desirable characteristics mentioned above.

It is an additional object of the invention to provide a new and improved direction-indicating system the operation of which is prem-'sed on average values of wave-signal'travel diierentials for effecting indications of direction and one which, therefore, is not affected either by any normal slow changes of intensities of received wave signals or rapid changes of intensity of relatively short duration.

In accordance with the invention, there is provided in a radiant-energy system of. the type which effects translation of a modulation signal over at least two space paths extending between an antenna of one antenna system and individual antennas of another antenna system, a direction-indicating device for indicating with relation to a predetermined reference plane the direction of one of the antenna systems relative to the other. This device comprises means responsive to thc modulation signals translated over the aforementioned space 1ilaths for developing a pair of signals having characteristics which vary similarly with time and a time relationship varying with the relative lengths of the space paths. The device includes means for differentially combining these developed signals to derive a control signal effectively of pulse wave form and having a pulse duration varying with the time relationsnip of the developed signals, and means responsive to the control signal for indicating the direction of one of the aforesaid antenna systems relative to the other.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring now to the drawings, Fig. l is a circuit diagram, partly schematic, of a complete direction-indicating system embodying the present invention; Figs. 2 and 3 are curves used as an aid in explaining the operation of the invention; and Figs. 4 and 5 represent direction-indicating systems embodying modified forms of the invention.

Referring now more particularly to Fig, l of the drawings, there is represented a complete direction-indicating system embodying the present invention in a particular form suitable for providing an indication of direction with relation to a predetermined reference plane of longitude which is coincident with a iixed terrestrially positioned antenna system of the indicating system. This arrangement thus provides azimuthal indications. It will be understood, however, that the invention is not so limited and the reference plane may, if desired, he a horizontal one in;

which case the indications then involve the aspect of elevational direction. This system includes a pair of spaced antennas i i, il? coupled to individual ones of a pair of transmitters i3, i4 for generating and transmitting individual ones of a pair of carrier-wave signals. Each of the transmitters i3, iii includes a modulationr input circuit coupled to an output circuit of a pulse generator l5, which. `generates a signal of periodicpulse wave form. The system also includes a second pair of spaced antennas l, Il coupled to individual ones of a pair of transmitters la' i9, which also have individual modulation input circuits coupled to an output circuit of generator l5. Antennas il, l2, l5 and il? are preferably located on a Cartesian system of coordinates, passing through the four cardinal points of the compass, and equidistant from the origin thereof, Transmitters i3, is, l and i9 are oi the pulse-modulated type and have individual carrier-wave frequencies. It will be understood that the elements li-ll, inclusive, are normally terrestrially located, and that the portion of the system presently to loe described is normally associated with a craft the direction of which is to be determined and comprises a direction-indicating device for receiving the wave signals radiated from antennas il, i2, I6 and il to indicate its direction with respect to these antennas. Since the antennas il, l2, l and lll are xed and are spaced along axes having known azimuthal bearings, the course indications provided by the system become azimuthal indications and will be hereinafter referred to as such.

The direction-indicating device includes means for selectively receiving wave signals from antennas il and i2. This means is coupled to a receiving antenna system 2b and comprises two similar wave-signal translating channels, componente of the second channel corresponding to analogous components of the first channel being designated by similar reference numerals primed. The first channel comprises in cascade, in the order named, a radio-frequency amplifier 2|, an oscillator-modulator 23 for convertingthe received wave signals to intermediate-frequency signals, and an intermediate-frequency amplifier 23 which preferably includes at least one amplitilde-limiter stage for limiting to a predetermined value the amplitude of the pulse-modulated wave signal translated by unit 23. rlhe output circuit of unit 23 is coupled to an input circuit of a control-signal generator 2d. The rst channel, comprising units 2l-23, inclusive, selectively receives and translates the wave signal of transmitter I3, while the second channel, comprising units 2i-23, inclusive, selectively receives and translates the wave signal of transmitter I4.

The unit 2t includes a pair of input transformers 25 and 2li having primary windings couple to the output circuits of the respective ampliers 25S and 23. These transformers have secondary windings 25, 26 which are tuned by respective condensers 2l and 2l to provide frequency-selective circuits 2li, 21 and 28', 21 resonant at the nominal intermediate frequencies of the respective ampliers 23 and 23.

The direction-indicating device also includes a pair of rectifier systems having individual load impede-noos for deriving across the latter the modulation components of the wave signals from antennas Il and l2. One rectifier system com prises a diode rectifier 3E) and a load resistor 3| therefor, these components being serially connected across the frequency-selective circuit 25, 2l. The other rectifier system similarly cornprises a diode rectier 3G and a load resistor 3l' which are serially connected across the frequency-selective circuit 2B', 2T.

The device additionally includes energy-storage means coupled to individual ones of the load resistors 3l, and responsive to the derived modulation components of the received wave signais for developing a pair of signals having characteristics'which vary similarly with time. This means comprises a pair of condensers 32, 32 individually connected in parallel with resistors 3l, El respectively.

Means is provided for diierentially combining the signals developed by condensers 32, 32 to derive a first control signal eiectively of pulse wave form. This means comprises the control electrode and cathode elements of a-Dair ofvacuum tubes 3E and S. The cathodes of these vacuum tubes are connected to gro-und, whereas their control electrodes are connected to individual terminals of the load impedances 3i, 32 and 32', 32' of the respective diode rectiflers d and 3d', these load impedances having a common termina1 and the diode rectiilers being so po-led that the potentials developed acrossfthe uncommon terminals of the load impedances have the same polarity. A grid-leak resistor 33 is connected between the control electrode and cathode of the vacuum tube 3% to serve as a common grid-leak resistor for both of the vacuum tubes 36 and 3S'. It may be noted that this common grid-leak resistor may be con'- nected between ground and any point on the circuit which includes the elements 3l, 32, 3|' and 32'.

The direction-indicating device additionally includes means responsive to this first control signal for indicating the azimuth of the indicating device relative to the antennas I I, I2. This means includes means for developing from this control signal a second control signal having a characteristic varying with the pulse duration of the first control signal. This last-mentioned means comprises a time-constant circuit including 'a condenser 31 connected across the output electrodes of tube 36, together with a resistor 38 of relatively large value connected between the anode of this tubey and a source of energizing potential, indicated as -l-B, and a similar time-constant circuit including a condenser 31 connected across the output electrodes of tube 36' and a resistor 3S of relatively large value connected between the anode of the latter tube and the potential source +B.

The first control-signal responsive means also includes means for developing from the second control signal a third control signal having a characteristic varying with a characteristic of the second control signal. The last-named means comprises a pair of vacuum tubes 3S, 3S', having their control electrodes coupled to respective ones of the output circuits of tubes 36 and 36', and cathode-circuit time-constant networks including a condenser di! and parallel-connected resistor 4i for the tube S9 and a condenser 49 and parallelconnected resistor lil for the tube 39. The

anodes of tubes 39, 39' are energized from an anode-potential source, indicated as -l-B.

In order to provide for visual directional indications, the output circuit of control-signal generator 24 is coupled to the vertical beam-defiecting elements of a cathode-ray tube 42. rlube 42 is of a conventional type and is provided with suitable operating potentials, not shown for simplicity.

It wl be seen that the units 2I-23, inclusive, 2I23, inclusive, and 26 are adapted to receive wave-signal energy from the north-south antennas II-I2, so that they may be referred to as the north-south receiving system.

The` direction-indicating device further includes an east-west receiving system d3, which has an input circuit coupled to the common receiving antenna 2G. Receiving system @3, which includes circuit elements similar to those of the northsouth receiving system, is adapted to receive and to translate tol an associated control-signal generator 44 wave-signal energy from antennas I6, I1. Generator 4d comprises elements similar to those included in unit 2d and a similar circuit arrangement. The output circuit of generator 44 is coupled to the horizontal beam-deecting elements of tube 42.

Considering now the operation of the indicating system just described, the wave signals of the transmitters I3, i4, IB and i9 are smultaneously modulated by a signal of periodic-pulse wave form generated by the generator I5, thus to radiate pulse-modulated wave signals distinguishable in frequency. Assume that the direction-indicating deviceis inthe north-east quadrant. The signals from transmitters i3 and i 4, hereinafter referred to as the "north and south signals, respectivey, are selectively received by the respectiveradio-frequency amplifiers 2| and 2|', converted into intermediate-frequency signals by the units 22 and 22', amplified at intermediate frequency by the amplifiers 23 and 23', and applied to the input-circuit transformers 25 and 25 of unit 24. It is assumed that the distance from the antennas I2, I I to the indicating device is so great that the convergence of the paths of signal travel from antennas I2, II to antenna 20 may be neglected. Under the assumed conditions, the pulsemodulation components of the wave signals received from the north and south transmitters I3 and i4 have a relative time displacement at the time of reception given by the relation:

t=kd sin a (1) where d is the distance between antennas II a-nd I2,

c is the angle formed by a line drawn from antenna 2U to the midpoint of the line between antennas I6 and I'I, and

1c isa constant related to the wave-signal velocit and the units of measurement selected.

t'=kd cos a (2) As will presently be explained in greater detail, the system has such operation that control signals are applied to cathode-ray tube 42 having values varying with the signal-time differentials lcd sin a and kd cos a, thus to provide direction indications through a BSO-degree angle and with out ambiguity.

The manner in which the control signals just mentioned are derived from the received wavesignal energy will now be considered in connection with the curves of Fig. 2 which represent the wave forms of voltages appearing at selected points in the direction-indicating device. Consider for the moment only the wave-signal modulation components corresponding to a single given pulse of the signal of generator I5. Under the conditions heretofore assumed, the wave-signal modulation components from the north transmitter I3 are the first ones to arrive at the direction-indicating device. These components are translated through receiver units 2I23, inclusive, to the signal generator 24. The received Wave signal is of the pulse-modulation type and is preferably limited to a substantially constant amplitude by the amplitude-limiter stage or stages included in the amplier 23, thus to reduce the effect of undesirable changes of received wavesignal intensity. The received Wave signal is translated by the frequency-selective circuit 26, 2l and is applied to the diode rectifier 3Ilwhich derives the modulation components thereof. If the condenser 32 were disconnected from the load resistor 3|, the derived pulse-modulation components would produce across the latter resistor at time t1, Fig. 2, a potential pulse having the wave form represented by curve A of Fig. 2. With the condenser 32 connected across the resistor 3l, however, the derived pulse rapidly charges the latter during the pulse interval. At the termination of the pulse, condenser 32 discharges slowly through the relatively large resistor 3l to develop thereacross a signal having an exponential portion, as represented by curve B.

This developed signal is applied between the control electrodes of tubes 36 and 36 and has positive polarity with respect to the control electrode of tube 35. The control electrode of tube 35 becomes conductive as soon as it is biased only slightly positive with respect to its cathode. Further, the potential drop between the control electrode and cathode of tube 36 then becomes so small that the control electrode cannot be biased more than a small fraction of a volt positive with relation to the cathode. Consequently, the control electrode of tube 36 is maintained at substantially ground potential, which is the potential of the cathode of this tube, during the application thereto of the signal developed across the condenser 32 so that the signal is applied With substantially full amplitude and negative polarity between thee control electrode and cathode of vacuum tube 35', as represented by curve C. In this regard, it should be noted that in the absence of any received wave-signal energy, the control electrodes of vacuum tubes 3@ and 36 have substantially zero bias with respect to their associated cathodes and both of these tubes are fully conductive under this condition. The resistors 38 and 38 in the anode circuits of the latter have values suiiiciently high that the potential drops produced across these resistors by the zero-bias space currents of tubes 36 and 3G' are so large that only a small positive potential is actually applied to the anodes of these tubes. Consequently, ie signal derived across the condenser 32 is not repeated with any substantial amplitude to the output circuit of the tube 35, due to the low anode potential of the latter, but is repeated to the output circuit of the tube 36' since it causes the control electrode of this tube to become more negative with relation to its associated cathode, thus reducing the space current of tube 35 and thereby tending to increase its anode potential. In practice, the amplitude of the signal developed across the condenser 32 preferably is sufliciently large that it causes the control electrode of vacuum tube 30 to bias the latter to or beyond anode current cutoff so that undesirable changes of amplitude of the signal, as might be caused by undesirable changes of received Wave-signal intensity, are not eifective to vary the amplitude of the signal developed in the output circuit of the tube 3%.

At some later time, for example at time t2 of Fig. 2, the Wave signal radiated by the antenna l2 of the south transmitter I4 is received by the indicating device; is translated through the receiver units 2I-23, inclusive; is limited to a substantially constant vamplitude by .the amplitudelimiter stage of the unit 23'; and is applied through the frequency-selective circuits 26', 2l to the diode rectier Sil which derives the modulation components thereof. Were it not for the condenser 32', there would thus be developed across the resistor 3l' a potential of pulse Wave form, as represented by curve D of Fig, 2. The condenser 32', however, rapidly charges during the pulse and slowly discharges exponentially through resistor 3l' at the termination of the pulse, lthus to develop thereacross a signal, represented by curve E, having an exponential portion similar to that of the signal developed across the condenser 32 associated with the diode rectifier 3i?. The signal developed across 4the condenser 32 is applied between the control electrodes of vacuum tubes 36 and 36', but has a polarity opposite to that of the signal developed across the condenser 32 and thus one which tends -to restore the potential of the control electrode of tube 3E' to the same potential as its associated cathode. It will be apparent that the maximum value of the time interval ti-tz occurs when the indicating device is either due south or due north of the antennas Il, I2. The decrease of amplitude of the signal vdeveloped across the condenser 32, due to the discharge of the latter through the resistor 3 l, is sufficiently small even during the longest possible interval ti-ta last mentioned, that the signals developed across the condensers 32 and 32' have approximately equal amplitudes at time tz. The signal developed across the condenser 32 thus effectively terminates the signal developed across the condenser 32 so that there is applied to the control electrode of tube 36 a potential or control signal of pulse wave form, represented by curve F, having a pulse duration varying with the time interval ti-ta Expressed in another manner, the pulse duration of the control signal resulting from the differential combination of the signals developed across the condensers 32 and 32' has a value varying with lcd sin a.

The control signal applied to the control electrode of vacuum tube 36' renders the latter nonconductive during the pulse interval of the signal, .thus tending to increase the anode potential of this tube as previously mentioned. The anode potential does not increase at once, however, since the charge of the condenser 3l must correspondingly increase and the latter can only charge through the resistor 3S' of relatively large value. The circuit parameters are so selected that the time constant of the condenser 3l and resistor 38' is long compared to the pulse duration of the control signal applied to the control electrode of vacuum tube 3S. At the termination of a pulse of this control signal, condenser 3l' discharges rapidly through vacuum tube 3i which, as previously explained, again becomes conductive at the termination of the pulse. There is thus developed across the condenser 3l' a second control signal having positive polarity with respect to ground and having an approximately triangularpulse wave form, as represented by curve G. This second control signal has an amplitude varying substantially only With the pulse duration of the rst control signal applied to the control electrode of tube 36', and thus has an amplitude proportional to lcd sin a.

This second control signal is applied with positive polarity to the control electrode of tube 39'. The cathode resistor 4l' of this tube has a relatively large value, of the order of one megohm, and the cathode condenser l a capacitance only large enough to provide therewith a time constant three or four times the period of the second control signal. The circuit parameters are thus so chosen that, under no-signal conditions, condenser ii' is charged to such a potential that the cathode of tube 39' is more positive than its control electrode by an amount almost sufficient; to bias tube 39 to anode current cutoff. Upon the application of the second control signal, tube 39 becomes more conductive during the first several pulses thereof and condenser dil' receives an increment of charge to raise the cathode potential above the maximum amplitude of the second control signal by a value equal approximately to the anode current cutoff potential of tube Sil'. As indicated by curve H of Fig, 3, ythe condenser 40 charges rapidly during each pulse G' of the second control signal and discharges relatively slowly through the cathode resistor 4|'. A third unidirectional control signal thus is developed in the output or cathode circuit of tube 39', the magni- `tu'de of this control signal varying with the amplitude of the second control signal and thus being proportional to kd sin a.

This third control signal is applied to the vertical deecting electrodes of tube 42 to deflect the beam thereof in the Vertical direction, indicated in Fig. 1, by an amount proportional to lcd sin a. It may be noted in passing that the polarity of this control signal, considered with relation tol a selected one of the vertical deilecting electrodes of tube 42, is the same as long as the indicating device is positioned in either the north-east or north-west quadrants since corresponding modulation components of the Wave signal of antenna II then always precede those of the wave signal of antenna I2.

Similarly, wave signals from antennas I6,4 vIl are received by the east-west receiving system 43 and applied to control-signal generator 44. .Generator 44 derives the modulation components of the received wave signals and responds thereto to generate a control signal having a magnitude proportional to lcd cos a.. This control signal is applied to the horizontal beam-deiiecting electrodes of tube 42v to deflect the beam thereof in the horizontal direction as indicated in Fig. l. It may again be noted in passing that the polarity of this control signal considered relative to the horizontal deilecting electrodes is the same Whether the indicating device be inthe northeast or south-east quadrants since corresponding modulation components of antenna I6 then precede those of antenna I'I.

The two control signals thus applied to the deflecting electrodes of tube 42 simultaneously deflect the beam of the tube so that there appears on the screen thereof a luminous spot, the angular position of which indicates the direction of the indicating device with relation to the spaced antennas II, I2, I6 and I1. The screen of tube 42 may therefore be calibrated in terms of direction.

vIt will be apparent from the foregoing description of the system operation that when the direction-indicating device is in the south-east quadrant with relation to the spaced antennas, the first modulation-signal components to arrive at the indicating device are those of the antennaJ I2. The iirst developed signal in point of time consequently i-s that produced by condenser 32,. The second signal derived in point of time is that across the condenser 32 and this signal is diierentially combined with the rst developed signal in the input circuit of tubes 36 and 36' to derive a control signal of negative polarity as applied to the vcontrol electrode of tube 36. Tube '35' does not repeat this signal, but tubes 36 'and 39V and their associated circuits then function in similar manner to that previously described in connection with tubes 36 and 39 to develop al of the beam of tube 42 in a horizontal direction opposite to that hereinbefore described. f 1 Y The direction-indicating system has been de scribed as` including a plurality orv t ransnriitters VV ground installation. An additionally modied I3, I4, I8 and I9 coupled to the antenna systems Il, lf2, I B and I?, these elements normally comprising a terrestrially located system, operating in conjunctionwith the direction-indicating device comprising elements Qi'B-s, inclusive, 42, 43 and 44 normally carried by a craft the direction of which is to be indicated. It will be apparent, however, that an equally useful form of directionindicating system embodying the invention is, as shown in Fig. 4, one in which the spaced antennas Ii,'!2, it rand I terrestrially located, are coupled to individual ones of the input circuits of the plurality of Wave-signal translating channels 45, 45 of the receiving system and in which the transmitting system is carried by the craft and includes a single nondirective antenna 47 coupled to a single transmitter 48 having an amplitude-modulation input circuit coupled to a pulse generator I5. In this form of indicating system, the transmitter operates 'at only one wave-signalirequency andthe several Wavesignal translating channel-s of the receiving system are tuned-to receive wave signals of this frequency, Indications of the direction of the craft are here providedby the indicator 42 at the form of thissystem, shown in Fig. 5, is one in whichthe single transmitter 48 is terrestrially located and the spaced antennas and receiving system 49 are carried by the craft, thus to provide a homing type of indicating system.

From the above description of the invention, it will be apparent that the direction-indicating system is of the radiant-energy type which effects translation of a modulation signal or periodicpulsewave form over at least two space paths extending'between an antenna of one antenna system and individual spaced antennas of another antenna system. Further, it will be apparent that the indicating device is responsive to the modul'ation'signals translated over these space paths for developing a pair of signals having characteristics which vary similarly with time and which havea time relationship varying with the relative lengths of the space paths, thus to permit the differential combination of the developed signals to derive a control signal which is utilized in effecting the desired direction indication.

A direction-indicating device embodying the invention-:has the advantage that it is adapted for operation in a direction-indicating system of the pulse-modulation type and thus possesses all of the'advantages characteristic of pulse-modulation operation; namely, the operation of transmitting equipment of the system with high power gain 'and the operation of the system as a whole as a transponder type of system. hereinbeore mentioned. An indicating device embodying the invention has the additional advantage that its operation is not detrimentallyaffected by relatively slow changes of received wave-signal intensity, Such as might occur during conditions of severe atmospheric fading and the like. Nor is its operation 'affected by Arelatively rapid changes of received wave-signal intensity such as might occur by virtue of ymultiple paths of transmission or reception, or both in the transponder type'of operation, and to a. rapid change in the character of vsuch multiple paths due to relative movement of the indicating device and the transmitting equipment, as during the course of flight of an aircraft. The lack of sensitivity of the indicating device to` relatively slow changes of received wave-signal intensity is due of course, to the limiting action provided by the units 23 and 23 and to the operation of tubes 36 and 36. The lack of sensitivity of the indicating device to relatively rapid changes of Wave-signal intensity is due to the long time constant of the elements all, il and 4B', 4| in the cathode circuits of the respective vacuum tubes 39 and 3S which are sumciently long that the potentials developed thereacross vary only with the average values of amplitude of the control signal applied to the latter tubes.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore aimed to cover all such changes and modications as fall within the true spirit and scope of the invention.

What is claimed is:

l. In a radiant-energy system of the type which eiTects translation of a modulation signal over at least two space paths extending between an antenna of one antenna system and individual spaced antennas of another antenna system, a direction-indicating device for indicating with relation to a predetermined reference plane the direction of one of said antenna systems relative to the other comprising, means responsive to the modulation signals translated over said space paths for developing a pair of signals having characteristics which vary similarly with time and a time relationship varying with the relative lengths of said space paths. means for differentially combining said developed signals to derive a control signal eiectively of pulse Wave form and having a pulse duration varying with the time relationships of said developed signals, and means responsive to said control signal for indicating said direction.

2. In a radiant-energy system of the type which eiects translation of a modulation signal over at bining said developed signals to derive a control signal effectively of pulse wave form and having a. pulse duration varying with the time relationships yof said developed signals, and means responsive to said control signal for indicating said direction.

4. In a radiant-energy system of the type which effects translation of a modulation signal over at least two space paths extending between an antenna of one antenna system and individual spaced antennas of another antenna system, a direction-indicating device for indicating with relation to a predetermined reference plane the direction of one of said antenna systems relative to the other comprising, means responsive to the modulation signals translated over said space paths for developing a pair of signals having characteristics which vary similarly with time and a time relationship varying with the relative lengths of said space paths, means for diierentially combining said developed signals to derive a control signal effectively of pulse wave form and least two space paths extending between an antenna of one antenna system and individual spaced antennas of another antenna system, a direction-indicating device for indicating with relation to a predetermined reference plane the direction of one of said antenna systems relative to the other comprising, means responsive to the modulation signals translated over said space paths for developing a pair of signals having characteristics which vary similarly with time and a time relationship varying with the relative lengths of said space paths, means for differentially combining said developed signals to derive a control signal of approximately rectangularpulse wave form having a pulse duration varying with the time relationships of said developed signals, and means responsive to said control signal for indicating said direction.

3. In a radiant-energy system of the type which eiects translation of a modulation signal over at least two space paths extending between an antenna of one antenna system and individual spaced antennas of another antenna system, a direction-indicating device for indicating with relation to a predetermined reference plane the direction of one of said antenna systems relative to the other comprising, means responsive to the modulation signals translated over said space paths for developing a pair of signals of approximately saw-tooth wave form having amplitudes which vary similarly with time and having a time relationship varying with the relative lengths of said space pathameans for differentially comhaving a pulse duration varying with the time relationships of said developed signals, means for developing from said control signal a second control signal having a characteristic varying with the pulse duration' of said first control signal, and means responsive to said second control signal for indicating said direction.

5. In a radiant-energy system of the type which effects translation of a modulation signal over at least two space paths extending between an antenna of one antenna system and individual spaced antennas of another antenna system, a direction-indicating device for indicating with relation to a predetermined reference plane the direction oi' one of said antenna systems relative to the other comprising, means responsive to the modulation Isignals translated over said space paths for developing a pair of signals having characteristics which vary similarly with time and a time relationship varying with the relative lengths of said space paths, means for differentially combining said developed signals to derive a control signal effectively of pulse wave form and having a pulse duration varying with the time relationships of said developed signals, means for developing from said control signal a second control signal having an amplitude varying with the pulse duration of said iirst control signal, and means responsive to the amplitude of said second control signal for indicating said direction.

6. In a radiant-energy system cf the type which effects translation of a modulation signal over at least two space paths extending between an antenna of one antenna system and individual spaced antennas of another antenna system, a direction-indicating device for indicating with relation to a predetermined reference plane the direction of one of said antenna systems relative to the other comprising, means responsive to the modulation signals translated over said space paths for developing a pair of signals having characteristics which vary similarlr with time and a time relationship varying with the relative lengths of said space paths, means for differentially combining said developed signals to derive a control signal effectively of pulse waveV form and having a pulse duration varying with the time relationships of said developed signals, means forv developing from said control signal a second control signal of approximately triangular-pulse wave form having a characteristic varying with the pulse duration of said first control signal, and means responsive to said second control signal for indicating said direction.

7. In a radiant-energy. system of the type which effects translation of a modulation signal over at least two space path-s extending between an antenna of one antenna system and individual spaced antennas of another antenna system, a direction-indicating device for indicating with relation to a predetermined reference plane the direction of one of said antenna systems relative to the other comprising, means responsive to the modulation signals translated over Isaid space paths for developing a pair of signals having characteristics which vary similarly with time and a time relationship varying with the relative lengths of said space paths, means for differentially combining said developed signals to derive a control signal eiTectively of pulse wave form and having a pulse duration varying withthe time relationships of said developed signals, means for developing from said control signal a second control signal having an amplitude varying with the pulse duration of said first control signal, means for developing from Said second control signal a unidirectional control potential having a magnitude varying with the amplitude of said second control signal, and means responsive to said unidirectional potential for indicating said direction.

8. In an azimuth-indicating system of the type including at least one transmitter and a pair of spaced antennas for transmitting individual ones of a pair of wave signals modulated by individual modulation signals having a de' terminable time relation therebetween, a direction-indicating device for receiving said Wave signals to indicate with relation to a predetermined reference plane its direction with respect to said antennas comprising, means for selectively receiving said wave signals and responsive to the modulation components there-of for developing a pair of Isignals having characteristics which vary similarly with time and a time relationship Varying with the relative times of reception of the modulation components of said received wave signals, means for differentially combining said developed signals to derive a control signal eiectively of pulse wave form having a pulse duration varying with the time relationships of said developed signals, and means responsive to said control signal for indicating the direction of said indicating device relative to said spaced antennas.

9. In a direction-indicating system of the type including at least one transmitter and a pair of spaced antennas for transmitting individual ones of a pair of wave signals modulated by individual modulation signals having a determinable time relation therebetween, a direction-indicating device for receiving said wave signals to indicate with relation to a predetermined reference plane its direction with respect to said antennas comprising, means for selectively receiving said wave signals and for deriving from the modulation components thereof a pair of signals having characteristics which vary similarly with time and a time relationship varying with the relative times of reception of the mo-dulation components of said received wave signals, means for differentially combining said developed signals to derive a control signal eiectively of pulse wave form having a pulse duration varying with the time relationships of said developed signals, and means responsive to said control signal for indieating the direction of said indicating device relative to said spaced antennas.,

l0. In a direction-indicating system of the type including at least one transmitter and a pair of spaced antennas for transmitting individual ones of a pair of wave signals modulated by individual modulation signals having a determinable time relation therebetween, a direction-indicating.de- -vice for receiving said Wave signals to indicate with relation to a predetermined reference plane its direction with respect to said antennas comprising, meansfor selectively receiving said wave signals and for deriving the modulation cornponents thereof, means responsive to said derived modulation components for developing a pair oi signals having characteristics Which vary similarly with time and a time relationship varying with the relative times of reception oi the modulation components of said received wave signals, means for differentially combining said developed signals to derive a control signal effectively oi pulse-wave form having a pulse duration varying with the time relationships of said developed signals, and means responsive to said control signal for indicating the direction of said indicating device relative to said spaced antennas.

11. In a direction-indicating system of the type including at least one transmitter and a pair of spaced antennas for transmitting individual ones of a pair of wave signals modulated by individual modulation signals having a determinable time relation therebetween, a directioneindicating device for receiving said wave signals to indicate with relation to a predetermined reference plane its direction with respect to said antennas comprising, means for selectively receiving said wave signals and for deriving the modulation components thereof, energy-storage means responsive to said derived modulation components for developing a pair of signals of approximately sawtooth Wave form having amplitudes which vary similarly with time and a time relationship varying with the relative times of reception of the modulation components of said received. wave signals, means for differentially combining said developed signals to derive a control signal effectively of pulse Wave form having a pulse duration varying with the time relationships of said developed signals, and means responsive to said control signal for indicating the direction of said indicating device relative t0 said spaced antennas.

l2. In a direction-indicating system of the type including at least one transmitter and a pair of spaced antennas for transmitting individual ones of a pair of wave signals modulated by individual modulation signals having a determinable time relation therebetween, a direction-indicating device for receiving said Wave signals to indicate ith relation to a predetermined reference plane its direction with respect to said antennas comprising, means for selectively receiving said Wave signals, a pair of rectifier' systems including individual load impedances for deriving across said load impedances the modulation components of individual ones of said wave signals, a pair of energy-storage devices coupled to individual ones of said load impedances for deriving from said modulation components a pair of signals having characteristics which vary similarly with time and a time relationship varying with the relative times of reception oi the modulation components of said received wave signals, means for differentially combining said developed signals to derive a control signal eiectively of pulse wave form havingl a pulse duration varying with the I5 time relationships of said developed signals, and means responsive tosaid control signal for indieating the direction of said indicating device relative to said spaced antennas.

13. In a direction-indicating system of the type including at least one transmitter and va pair of spaced antennas for transmitting individual ones of a pair of wave signals modulated by individual modulation signals having a determinable time relation therebetween, a direction-indicating device fer receiving said wave signals to indicate with relation to a predetermined reference plane its direction with respect to said antennas comprising, means for selectively receiving said wave signals and responsive to the modulation cornponents thereof for developing a pair of signals having characteristics which vary similarly with I6 time and a time relationship varying with the relative times of reception of the modulation components of said received Wave signals, said means including a pair of serially-connected output circuits to which individual ones of said de.- veloped signals are applied, a pair of vacuum tubes having input electrodes al1 coupled in series relation across said output circuits to derive by differential combination of said developed signais a control signal effectively of pulse wave form having a pulse duration varying with the n time` relationships of said developed signals, and meansA responsive to said control .signal for indicating the direction of said indicating device relative to said spaced antennas.

BERNARD D. LOUGHLIN. 

